diff --git a/.gitignore b/.gitignore
index 0e9416e..223c0f4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,4 @@ examples/basic/dist/
 coverage/
 .DS_Store
 EVAL-CHECKLIST.md
+.worktrees/
diff --git a/.prettierignore b/.prettierignore
index 6cc72db..72882a1 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -1,5 +1,7 @@
 dist/
 node_modules/
+# Git worktrees for other branches; each one is checked in its own checkout.
+.worktrees/
 examples/glean/dist/
 examples/glean/plugins/
 examples/basic/dist/
diff --git a/eslint.config.js b/eslint.config.js
index b5660a4..0f818b8 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -6,6 +6,8 @@ export default tseslint.config(
     ignores: [
       "dist/**",
       "node_modules/**",
+      // Git worktrees for other branches; each one is linted in its own checkout.
+      ".worktrees/**",
       "examples/basic/dist/**",
       "examples/glean/dist/**",
       "examples/glean/plugins/**",
diff --git a/vitest.config.ts b/vitest.config.ts
index 58b94e3..17a760a 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -1,7 +1,9 @@
-import { defineConfig } from "vitest/config";
+import { configDefaults, defineConfig } from "vitest/config";
 
 export default defineConfig({
   test: {
+    // Git worktrees for other branches hold their own copies of the tests.
+    exclude: [...configDefaults.exclude, ".worktrees/**"],
     // Many tests run real builds, validations and packed CLIs against temp
     // projects. They take 1-4s locally, and the shared CI runners run the
     // suite in parallel at a fraction of that speed, so vitest's 5s default